Incidence of stroke is the #1 cause of disability in America and is disproportionately high in Alaskan Native populations. Hibernating mammals provide an animal model of natural tolerance to profound (up to 90%) reductions in cerebral blood flow. The long term goal of this project is to elucidate mechanisms of neuroprotection during hibernation and arousal from hibernation. Anti-oxidants defense mechanisms and suppression of CNS activity via adenosine release or changes in ion channel densities provide hibernating brain tissue enhanced protection from oxidative stress and neuronal cell death. Aim 1 is to test the hypothesis that release of adenosine, an inhibitory neuromodulator, is associated with entrance into and exit from hibernation. This hypothesis will be tested by sampling interstitial adenosine during entrance, maintenance and exit from hibernation using quantitative microdialysis in brains of arctic ground squirrels. Our second aim is to test the hypotheses that a) voltage gated sodium channel density is decreased during hibernation, and, b) ATP regulated potassium channel density is increased during hibernation. Studies will focus on changes in the quantity of channel protein using radioligand binding and western blotting and mRNA using quantitative PCR. Aim 3 examines mechanisms responsible for neuroprotection using 3 models of stress or trauma, i) arousal from hibernation, ii) traumatic brain injury induced by insertion of a microdialysis probe and ii) an in vitro brain slice model of oxidative stress and excytotoxicity. Our final aim is to add a comparative dimension to experiments proposes in Aims 1 to 3 to investigate species-specific aspects of neuroprotection using hypoxia as a model of arousal from hibernation, traumatic brain injury and our in vitro slice model. The project will be conducted as an integrated and coordinated collaboration between investigators at the University of Alaska Fairbanks (UAF) and Case Western Reserve University (CWRU). The UAF component of the project will focus on animal studies utilizing UAF's unique access to arctic ground squirrels. The CWRU component will provide expertise and training in immunocytochemistry and molecular technique which will ultimately be transferred to UAF. The hypothesis to be tested through the integration of both components will allow the complementary expertise in hibernation physiology, neurochemistry, immunocytochemistry and molecular biology to be applied in a maximally productive and mutually beneficial way. The collaboration will also provide opportunities for students and fellows at UAF to obtain training in immunocytochemical techniques and molecular biology at CWRU. The results of the proposed research will lead to a better understanding of mechanisms of neuroprotection during hibernation. Hibernation offers an excellent mammalian model of tolerance to reduced cerebral blood flow and neurodegeneration. Better understanding of mechanisms of neuroprotection may lead to improved therapies for stroke and head trauma.